AGB 211: Livestock and Poultry Breeding (2+1)

MEASUREMENT OF COEFFICIENT OF RELATIONSHIP

The relationship between two animals is expressed as coefficient of relationship, symbolised by “R “. It measures the probable portion of genes that are the same for two individuals due to their common ancestors, over and above the base population.

Relationship may be two kinds.

1. Direct
2. Collateral

• Direct relationship: You are directly related to your father or mother. You and your father have 505 common genes and you and your mother have 505 common genes.
• Collateral relationship: You and your cousin’s are collateral relatives because you both have some common ancestors.

You and your cousin have the same grand parents C and D. The important step in measurement of relationship is the number of generations between the animals studied and that common ancestor.

The formula for relationship between individual X and Y is

R_xy =∑ [(1/2) ^n+n’ ]

Where

∑ = summation

½ = Halving of inheritance in each generation

n = No. of generations between X and the common ancestor or the no. of times the halving process has undergone between X and common ancestor

n’ = No. of generations between Y and the common ancestor or the no. of times the halving process has undergone between Y and common ancestor.  

EXAMPLES

1. Relationship between son and father

R_xy   = [(1/2)^n+n’ ]

= [(1/2)¹⁺⁰ ] = ½ or 50%

 

There is one generation between son and father and genetic material is halved once. There is no generation beyond father and hence n’ is zero.

2. Relationship between son and grand father

R_xy    = [(1/2)²⁺⁰ ]

= ½² =1/4 or 25%

There are two generations between son or (X) and grand father © and n=2. There is no generation beyond C and n’ = 0.

3. Relationship between brother / sister / brother and sister

First find the no. of common ancestors. In this example there are two common ancestors, A and B.

• Relationship through A

R_xy    = [(1/2)¹⁺¹ ]

= ½² =1/4 or 25%

• Relationship through B

R_xy    = [(1/2)¹⁺¹ ]

= ½² =1/4 or 25% 

sum of relationship = ½ or 50%

4. Relationship between first cousin

• Relationship through C

R_xy = [(1/2)²⁺² ]=1/16 or 6.25

• Relationship through D

R_xy = [(1/2)²⁺² ]=1/16 or 6.25

sum of relationship = 1/8 or 12.50%

5. Relationship between half first cousin

• Relationship through C only

R_xy = [(1/2)²⁺² ]=1/16 or 6.25

6. Relationship between double first cousins

• Relationship through C = [(1/2)²⁺² ]=1/16 = 6.25%
• Relationship through D = [(1/2)²⁺² ]=1/16 = 6.25%
• Relationship through I = [(1/2)²⁺² ]=1/16 = 6.25%
• Relationship through J = [(1/2)²⁺² ]=1/16 = 6.25%

Sum of relationship = 25.00%

Direct and collateral relationship simultaneously